The present invention is particularly useful in a plurality of embodiments of continuously variable transmission units of the type disclosed in U.S. Pat. No. 4,152,946 issued May 8, 1979 to Yves Kemper assigned to the Vadetec Corporation of Troy, Michigan. Such continuously variable transmission units, hereafter referred to as CVT units, are of the traction drive type and offer considerable promise for vehicular use.
In the general type of CVT unit referred to in the above-designated patent three working bodies operate to transmit torque to a rotatable output member at a continuously variable output/input speed ratio throughout a preselected range. The working bodies are represented by a first body having a pair of axially movable internal traction surfaces of revolution about a central axis, a second body having a pair of external cone-like traction surfaces of revolution about an inclined axis intersecting the central axis, and a third body journalled for rotation about the central axis and carrying the second body such that rotational torque applied to the third body causes the nutational movement of the inclined axis. If the first body is held stationary as a reaction and the third body is driven as an input member, the second body can have a nutating pinion gear coupled thereto which serves as the output to a gear train. Axial movement of the first body with respect to the cone-like traction surfaces of the second body results in modifying the speed ratio to the output desired. The technical performance and operating parameters of these transmissions are described in an American Society of Mechanical Engineers Article entitled "Performance of a Nutating Traction Drive" by P. Elu and Y. Kemper of Aug. 18-21, 1980 and identified as Paper No. 80-C2/DET-63.
The physical characteristics of many of these CVT units are such that relatively high efficiencies are obtained through a relatively narrow range of speed ratios. But, by linking an output gear train to two of the three bodies the range of speed ratios of the CVT unit can be broadened while maintaining relatively high efficiencies. One prior output gear train adapted to broaden the speed range is illustrated in FIGS. 1 and 7 of aforementioned U.S. Pat. No. 4,152,946 and embodies a set of three conical convex gears or external bevel gears having a common apex for connecting the second and third working bodies to an output shaft having one of the bevel gears thereon. Unfortunately, that set of external bevel gears exhibits a considerable gear tooth friction loss which decreases the overall efficiency of the CVT unit. Moreover, the set of external bevel gears is crowded so that the amount of space left for the support bearings for these gears is minimal. Still further, it is a relatively complex matter to adjust the axial positioning of the external bevel gears with respect to one another.
Accordingly, it would be advantageous to provide an improved gear train for use with a CVT unit of the aforementioned type which would broaden the speed range thereof, which would be of high efficiency such as by exhibiting an efficient gear tooth mesh, which would be relatively compact and yet have sufficient space for the supporting bearings, and which would be simple and economical in construction.
The present invention is directed to a gear train overcoming one or more of the problems as set forth above.